Bubbles sits under a cover the wife got off of Amazon last year, and over that a pop-up type awning (Eze-up type) that we got last year at Lowe's.
You can see the Eze-up in this pic from a few weeks ago:

Unfortunately, high winds are not uncommon in this part of the country and our Eze-up had already been damaged once. Finally, last Thursday a particularly strong series of gusts tore it up and flipped it into the neighbor's yard. And two days later we got the biggest snowstorm of the season, about a foot of heavy, wet snow:

Now, one thing we learned last year was to never, never, ever, let a wet cover sit on the wood! So the cover will be coming off tonight now that the snow has melted off. This will also allow the trailer to dry off.
Last year when we got back from Oregon we put a layer of deck sealant (thompson's water-seal) and over that a layer of polyurethane spar varnish. As you can see from the pic above (which was taken After bubbles had sat outside all winter) the finish still looks pretty good.
However, we're realistic: We understand that in this environment, we're going to probably have to figure on sanding and re-varnishing every year.
Also with regards to the cover (which is already torn in several places thanks to our too-sharp metal rain gutters) and the Eze-up, I think I've convinced Liz that we need to regard those like the bodyguards that surround a high-ranking official: They're "expendable." So I imagine we'll be buying a new eze-up and a new cover every year, but that's still a lot less expensive than renting a covered storage unit. In fact, I calculated it and if we bought a new cover every 6 months and a new Eze-up every year, it still wouldn't add up to half of what indoor storage would cost!